1. Field of the Invention
The present invention relates to a distortion-correcting circuit for decreasing the number of distortions in high-output amplification, an integrated circuit, and a radio communication device.
2. Description of the Related Art
A distortion-correcting circuit has been used so far in the past in order to decrease the number of distortions generated when amplifying signals.
The distortion-correcting circuit is mainly used to decrease the number of distortions in a high-output amplifier used for a radio-communication base station or a satellite-communication base station, that is, a high-output amplifier for a device using a wide frequency band (such as a multicarrier communication device).
In the case of the above high-output amplifier, when amplifying a wide-frequency-band signal such as a multicarrier signal, a distortion (CTB: Composite Triple Beat) occurs in addition to a desired wave (purposed output signal).
Therefore, when no distortion-correcting circuit is used, it is obliged to back off an operating point in a high-output amplifier in order to decrease the number of distortions. In this case, by forming the operating point into a linear region, a desired electrical characteristic is obtained and a distortion suppression characteristic is improved but the power added efficiency is deteriorated and much heat is produced. That is, when no distortion-correcting circuit is used, the power added efficiency and distortion suppression characteristic are kept in the relation of trade-off.
Therefore, to improve the power added efficiency and distortion suppression characteristic at the same time, a distortion-correcting circuit is used.
FIG. 14 is a block diagram showing a conventional distortion-correcting circuit 100.
In FIG. 14, the distortion-correcting circuit 100 is constituted by including a power distributor 110, a delay line 120, a power synthesizer 130, and a distortion-extracting section 140.
The power distributor 110 secures matching and isolation between input impedances and distributes powers of input signals (Pin) in order to prevent reflection and interference from occurring between the system of the delay line 120 of the distortion-correcting circuit 100 and the system of the distortion-extracting section 140 because impedances of the both systems are different from each other.
The delay line 120 matches the phase of a received signal with the phase of a signal input to the distortion-extracting section 140.
The power synthesizer 130 has a function reverse to that of the power distributor 110 and synthesizes two input signals (signal input from delay line 120 and signal input from distortion-extracting section 140).
The distortion-extracting section 140 is constituted by further including a power distributor 141, attenuators 142 and 146, amplifiers 143 and 145, and a power synthesizer 144.
The power distributor 141 has a function same as that of the power distributor 110 and distributes powers of signals input from the power distributor 110 to the distortion-extracting section 140.
The attenuators 142 and 146 respectively attenuate an input signal power by a set predetermined gain.
The amplifiers 143 and 145 respectively amplify an input signal power by a set predetermined gain.
The power synthesizer 144 has a function same as that of the power synthesizer 130 and synthesizes two input signals (signals output from two processing systems of distortion-extracting section 140).
In the above configuration, input signals (Pin) are distributed and input to the delay line 120 and distortion-extracting section 140 in the power distributor 110 and distortion components are extracted from input signals of the distortion-correcting circuit 100 of the distortion-extracting section 140. Then, distortion components are inverted and synthesized for input signals whose phases are matched by the delay line 120 in the power synthesizer 130 and thus, output signals (Pout) from which most distortions are removed are obtained.
However, because the conventional distortion-correcting circuit 100 uses passive components such as the power distributors 110 and 141, power synthesizers 130 and 144, and delay line 120, there is a problem that a circuit scale is increased because of these components. Though this problem can be admitted by a large communication device such as a radio-communication base station system, it becomes a large problem for a device which must be decreased in size or constituted by an integrated circuit such as a consumer product.